Method of controlling a dual clutch transmission

ABSTRACT

A method of controlling a hydraulic control system for a dual clutch transmission includes controlling a plurality of pressure and flow control devices in fluid communication with a plurality of clutch actuators and with a plurality of synchronizer actuators. The clutch actuators are operable to actuate a plurality of torque transmitting devices and the synchronizer actuators are operable to actuate a plurality of synchronizer assemblies. Selective activation of combinations of the pressure control solenoids and the flow control solenoids allows for a pressurized fluid to activate at least one of the clutch actuators and synchronizer actuators in order to shift the transmission into a desired gear ratio.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/420,157, filed Dec. 6, 2010. The entire contents of the aboveapplication are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a method of controlling a dual clutchtransmission, and more particularly to a method of controlling anelectro-hydraulic control system having a plurality of solenoidsoperable to actuate a plurality of actuators within the dual clutchtransmission.

BACKGROUND

A typical multi-speed, dual clutch transmission uses a combination oftwo friction clutches and several dog clutch/synchronizers to achieve“power-on” or dynamic shifts by alternating between one friction clutchand the other, with the synchronizers being “pre-selected” for theoncoming ratio prior to actually making the dynamic shift. “Power-on”shifting means that torque flow from the engine need not be interruptedprior to making the shift. This concept typically uses countershaftgears with a different, dedicated gear pair or set to achieve eachforward speed ratio. Typically an electronically controlled hydrauliccontrol circuit or system is employed to control solenoids and valveassemblies. The solenoid and valve assemblies actuate clutches andsynchronizers to achieve the forward and reverse gear ratios.

While previous hydraulic control systems are useful for their intendedpurpose, the need for new and improved hydraulic control systemconfigurations within transmissions which exhibit improved performance,especially from the standpoints of efficiency, responsiveness andsmoothness, is essentially constant. Accordingly, there is a need for animproved, cost-effective hydraulic control system for use in a dualclutch transmission.

SUMMARY

A method of controlling a hydraulic control system for a dual clutchtransmission includes controlling a plurality of pressure and flowcontrol devices in fluid communication with a plurality of clutchactuators and with a plurality of synchronizer actuators. The clutchactuators are operable to actuate a plurality of torque transmittingdevices and the synchronizer actuators are operable to actuate aplurality of synchronizer assemblies. Selective activation ofcombinations of the pressure control solenoids and the flow controlsolenoids allows for a pressurized fluid to activate at least one of theclutch actuators and synchronizer actuators in order to shift thetransmission into a desired gear ratio.

In one example, the method includes controlling an electric pump and anaccumulator that provide a pressurized hydraulic fluid.

In another example, the method includes controlling one pressure controldevice and two flow control devices used to actuate the dual clutch.

In yet another example, the method includes controlling one pressurecontrol device and four flow control devices used to actuate theplurality of synchronizer assemblies.

Further features, aspects and advantages of the present invention willbecome apparent by reference to the following description and appendeddrawings wherein like reference numbers refer to the same component,element or feature.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic diagram of an exemplary dual clutch transmissionhaving a hydraulic control system in accordance with the principles ofthe present invention;

FIGS. 2A and 2B are schematic diagrams of an embodiment of a hydrauliccontrol system for a dual clutch transmission in accordance with theprinciples of the present invention;

FIG. 3 is a flow diagram of a process for controlling an oil deliverysubsystem of the hydraulic control system of FIGS. 2A and 2B inaccordance with the principles of the present invention;

FIG. 4 is a diagram showing typical charge and discharge cycles of theoil delivery subsystem for accumulator pressure versus time;

FIG. 5 is flow diagram of a process for controlling a clutch controlsubsystem of the hydraulic control system of FIGS. 2A and 2B inaccordance with the principles of the present invention;

FIG. 6 is a diagram showing transient modes of a synchronizer of thetransmission of FIG. 1; and

FIGS. 7A and 7B are flow diagrams of a process for controlling asynchronizer control subsystem of the hydraulic control system of FIGS.2A and 2B in accordance with the principles of the present invention.

DESCRIPTION

With reference to FIG. 1, an exemplary dual clutch automatictransmission incorporating the present invention is illustrated andgenerally designated by the reference number 10. At the outset it shouldbe appreciated that the transmission 10 is illustrated schematically inorder to generally indicate some of the components of the transmission10. It should be appreciated that the illustration of the transmission10 is not intended to be limiting to the configuration shown. The dualclutch transmission 10 includes a typically cast, metal housing 12 whichencloses and protects the various components of the transmission 10. Thehousing 12 includes a variety of apertures, passageways, shoulders andflanges which position and support these components. While the housing12 is illustrated as a typical rear wheel drive transmission, it shouldbe appreciated that the transmission 10 may be a front wheel drivetransmission or a rear wheel drive transmission without departing fromthe scope of the present invention. The transmission 10 includes aninput shaft 14, an output shaft 16, a dual clutch assembly 18, and agear arrangement 20. The input shaft 14 is connected with a prime mover(not shown) such as an internal combustion gas or Diesel engine or ahybrid power plant. The input shaft 14 receives input torque or powerfrom the prime mover. The output shaft 16 is preferably connected with afinal drive unit (not shown) which may include, for example, propshafts,differential assemblies, and drive axles. The input shaft 14 is coupledto and drives the dual clutch assembly 18. The dual clutch assembly 18preferably includes a pair of selectively engageable torque transmittingdevices including a first torque transmitting device 22 and a secondtorque transmitting device 24. The torque transmitting devices 22, 24are preferably dry clutches. The torque transmitting devices 22, 24 aremutually exclusively engaged to provide drive torque to the geararrangement 20.

The gear arrangement 20 includes a plurality of gear sets, indicatedgenerally by reference number 26, and a plurality of shafts, indicatedgenerally by reference number 28. The plurality of gear sets 26 includesindividual intermeshing gears that are connected to or selectivelyconnectable to the plurality of shafts 28. The plurality of shafts 28may include layshafts, countershafts, sleeve and center shafts, reverseor idle shafts, or combinations thereof. It should be appreciated thatthe specific arrangement and number of the gear sets 26 and the specificarrangement and number of the shafts 28 within the transmission 10 mayvary without departing from the scope of the present invention. In theexample provided, the transmission 10 provides seven forward gears and areverse gear.

The gear arrangement 20 further includes a first synchronizer assembly30A, a second synchronizer assembly 30B, a third synchronizer assembly30C, and a fourth synchronizer assembly 30D. The synchronizer assemblies30A-D are operable to selectively couple individual gears within theplurality of gear sets 26 to the plurality of shafts 28. Eachsynchronizer assembly 30A-D is disposed either adjacent certain singlegears or between adjacent pairs of gears within adjacent gear sets 26.Each synchronizer assembly 30A-D, when activated, synchronizes the speedof a gear to that of a shaft and a positive clutch, such as a dog orface clutch. The synchronizer positively connects or couples the gear tothe shaft. The synchronizer actuator is bi-directionally translated by ashift rail and fork assembly (not shown) within each synchronizerassembly 30A-D. In certain arrangements two single-sided synchronizerscan be used in place of a double-sided synchronizer without departingfrom scope of the invention.

The transmission also includes a transmission control module 32. Thetransmission control module (TCM) 32 is preferably an electronic controldevice having a preprogrammed digital computer or processor, controllogic, memory used to store data, and at least one I/O peripheral. Thecontrol logic includes a plurality of logic routines for monitoring,manipulating, and generating data. The transmission control module 32controls the actuation of the dual clutch assembly 18 and thesynchronizer assemblies 30A-D via a hydraulic control system 100according to the principles of the present invention. It should beappreciated that the transmission control module 32 may be integratedinto other existing controllers without departing from the scope of thepresent invention. Turning to FIG. 2, the hydraulic control system 100of the present invention is operable to selectively engage the dualclutch assembly 18 and the synchronizer assemblies 30A-D by selectivelycommunicating a hydraulic fluid 102 from a sump 104 to a plurality ofshift actuating devices, as will be described in greater detail below.The sump 104 is a tank or reservoir to which the hydraulic fluid 104returns and collects from various components and regions of theautomatic transmission 10. The hydraulic fluid 102 is forced from thesump 104 via a pump 106. The pump 106 is preferably driven by anelectric engine (not shown) or any other type of prime mover and may be,for example, a gear pump, a vane pump, a gerotor pump, or any otherpositive displacement pump. The pump 106 includes an inlet port 108 andan outlet port 110. The inlet port 108 communicates with the sump 104via a suction line 112. The outlet port 110 communicates pressurizedhydraulic fluid 102 to a supply line 114. The supply line 114 is incommunication with a spring biased blow-off safety valve 116, a pressureside filter 118, and a spring biased check valve 120. The spring biasedblow-off safety valve 116 communicates with the sump 104. The springbiased blow-off safety valve 116 is set at a relatively highpredetermined pressure and if the pressure of the hydraulic fluid 102 inthe supply line 114 exceeds this pressure, the safety valve 116 opensmomentarily to relieve and reduce the pressure of the hydraulic fluid102. The pressure side filter 118 is disposed in parallel with thespring biased check valve 120. If the pressure side filter 118 becomesblocked or partially blocked, pressure within supply line 114 increasesand opens the spring biased check valve 120 in order to allow thehydraulic fluid 102 to bypass the pressure side filter 118.

The pressure side filter 118 and the spring biased check valve 120 eachcommunicate with an outlet line 122. The outlet line 122 is incommunication with a second check valve 124. The second check valve 124is in communication with a main supply line 126 and is configured tomaintain hydraulic pressure within the main supply line 126. The mainsupply line 126 supplies pressurized hydraulic fluid to an accumulator130 and a main pressure sensor 132. The accumulator 130 is an energystorage device in which the non-compressible hydraulic fluid 102 is heldunder pressure by an external source. In the example provided, theaccumulator 130 is a spring type or gas filled type accumulator having aspring or compressible gas that provides a compressive force on thehydraulic fluid 102 within the accumulator 130. However, it should beappreciated that the accumulator 130 may be of other types, such as agas-charged type, without departing from the scope of the presentinvention. Accordingly, the accumulator 130 is operable to supplypressurized hydraulic fluid 102 back to the main supply line 126.However, upon discharge of the accumulator 130, the second check valve124 prevents the pressurized hydraulic fluid 102 from returning to thepump 106 when the pressure in line 122 is less than line 126. Theaccumulator 130, when charged, effectively replaces the pump 106 as thesource of pressurized hydraulic fluid 102, thereby eliminating the needfor the pump 106 to run continuously. The main pressure sensor 132 readsthe pressure of the hydraulic fluid 102 within the main supply line 126in real time and provides this data to the transmission control module32.

The main supply line 126 is channeled through a heat sink 134 used tocool the controller 32, though it should be appreciated that the heatsink 134 may be located elsewhere or removed from the hydraulic controlsystem 100 without departing from the scope of the present invention.The main supply line 126 supplies pressurized hydraulic fluid 102 to twopressure control devices including a first clutch pressure controldevice 136 and an actuator pressure control device 140.

The first clutch pressure control device 136 is preferably anelectrically controlled variable force solenoid having an internalclosed loop pressure control. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thefirst clutch pressure control device 136 is operable to control thepressure of the hydraulic fluid 102. The first clutch pressure controldevice 136 includes an inlet port 136A that communicates with an outletport 136B when the first clutch pressure control device 136 is activatedor energized and includes an exhaust port 136C that communicates withthe outlet port 136B when the first clutch pressure control device 136is inactive or de-energized. Variable activation of the first clutchpressure control device 136 regulates or controls the pressure of thehydraulic fluid 102 as the hydraulic fluid 102 communicates from theinlet port 136A to the outlet port 136B. The internal closed looppressure control provides pressure feedback within the solenoid toadjust the amount of flow to the outlet port 1368 based on a particularcurrent command from the controller 32, thereby controlling pressure.The inlet port 136A is in communication with the main supply line 126.The outlet port 136B is in communication with an intermediate line 142.The exhaust port 136C is in communication with the sump 104 or anexhaust backfill circuit (not shown).

The intermediate line 142 communicates the hydraulic fluid 102 from thefirst clutch pressure control device 136 to a first clutch flow controldevice 144 and to a first pressure limit control valve 146. The firstclutch flow control device 144 is preferably an electrically controlledvariable force solenoid that is operable to control a flow of thehydraulic fluid 102 from the first clutch flow control device 144 inorder to actuate the first torque transmitting device 22, as will bedescribed in greater detail below. The first clutch flow control device144 includes an inlet port 144A that communicates with an outlet port144B when the first clutch flow control device 144 is energized to acurrent greater than the null point current (i.e. the current at thezero forward/reverse flow point) and includes an exhaust port 144C thatcommunicates with the outlet port 144B when the first clutch flowcontrol device 144 is de-energized to a current less than the null pointcurrent. Variable activation of the first clutch flow control device 144regulates or controls the flow of the hydraulic fluid 102 as thehydraulic fluid 102 communicates from the inlet port 144A to the outletport 144B. The inlet port 144A is in communication with the intermediateline 142. The outlet port 144B is in communication with a first clutchsupply line 148 and a flow restriction orifice 150 (which may or may notbe present). The exhaust port 144C is in communication with the sump104. The first pressure limit control valve 146 is disposed in parallelwith the first clutch flow control solenoid 144 and is in communicationwith the first clutch supply line 148. If pressure within the firstclutch supply line 148 exceeds a predetermined value above intermediateline 142, the first pressure limit control valve 146 opens to relieveand reduce the pressure. Pressure limit control valve 146 and thecorresponding parallel branch may be removed from the circuit if thefunctionality is not required and therefore does not depart from thescope of the invention.

The first clutch supply line 148 is in fluid communication with aninlet/outlet port 152A in a first clutch piston assembly 152. The firstclutch piston assembly 152 includes a single acting piston 154 slidablydisposed in a cylinder 156. The piston 154 translates under hydraulicpressure to engage the first torque transmitting device 22, shown inFIG. 1. When the first clutch flow control device 144 is activated orenergized, a flow of pressurized hydraulic fluid 102 is provided to thefirst clutch supply line 148. The flow of pressurized hydraulic fluid102 is communicated from the first clutch supply line 148 to the firstclutch piston assembly 152 where the pressurized hydraulic fluid 102translates the piston 154, thereby engaging the first torquetransmitting device 22. When the first clutch flow control solenoid 144is de-energized, the inlet port 144A is closed and hydraulic fluid fromthe cylinder 156 passes from the outlet port 144B to the exhaust port144C and into the sump 104, thereby disengaging the first torquetransmitting device 22. The translation of the piston 154 may bemeasured by a position sensor (not shown) for active control of thefirst torque transmitting device 22.

The intermediate line 142 also communicates the hydraulic fluid 102 fromthe clutch pressure control device 136 to a second clutch flow controldevice 160 and to a second pressure limit control valve 162. The secondclutch flow control device 160 is preferably an electrically controlledvariable force solenoid that is operable to control a flow of thehydraulic fluid 102 from the second clutch flow control device 160 inorder to actuate the second torque transmitting device 24, as will bedescribed in greater detail below. The second clutch flow control device160 includes an inlet port 160A that communicates with an outlet port160B when the second clutch flow control device 160 is energized to acurrent greater than the null point current and includes an exhaust port160C that communicates with the outlet port 160B when the second clutchflow control device 160 is de-energized to a current less than the nullpoint current. Variable activation of the second clutch flow controldevice 160 regulates or controls the flow of the hydraulic fluid 102 asthe hydraulic fluid 102 communicates from the inlet port 160A to theoutlet port 160B. The inlet port 160A is in communication with theintermediate line 142. The outlet port 160B is in communication with asecond clutch supply line 164 and a flow restriction orifice 166 (whichmay or may not be present). The exhaust port 160C is in communicationwith the sump 104 or a backfill circuit. The second pressure limitcontrol valve 162 is disposed in parallel with the second clutch flowcontrol solenoid 160 and is in communication with the second clutchsupply line 164. If pressure within the second clutch supply line 164exceeds a predetermined value above intermediate line 142, the secondpressure limit control valve 162 opens to relieve and reduce thepressure. Pressure limit control valve 162 and the correspondingparallel branch may be removed from the circuit if the functionality isnot required and therefore does not depart from the scope of theinvention.

The second clutch supply line 164 is in fluid communication with aninlet/outlet port 168A in a second clutch piston assembly 168. Thesecond clutch piston assembly 168 includes a single acting piston 170slidably disposed in a cylinder 172. The piston 170 translates underhydraulic pressure to engage the second torque transmitting device 24,shown in FIG. 1. When the second clutch flow control device 160 isactivated or energized, a flow of pressurized hydraulic fluid 102 isprovided to the second clutch supply line 164. The flow of pressurizedhydraulic fluid 102 is communicated from the second clutch supply line164 to the second clutch piston assembly 168 where the pressurizedhydraulic fluid 102 translates the piston 170, thereby engaging thesecond torque transmitting device 24. When the second clutch flowcontrol solenoid 160 is de-energized, the inlet port 160A is closed andhydraulic fluid from the cylinder 172 passes from the outlet port 160Bto the exhaust port 160C and into the sump 104, thereby disengaging thesecond torque transmitting device 24. The translation of the piston 170may be measured by a position sensor (not shown) for active control oftransmitting device 24.

The actuator pressure control device 140 is preferably an electricallycontrolled variable force solenoid having an internal closed looppressure control. Various makes, types, and models of solenoids may beemployed with the present invention so long as the actuator pressurecontrol device 140 is operable to control the pressure of the hydraulicfluid 102. The actuator pressure control device 140 includes an inletport 140A that communicates with an outlet port 140B when the actuatorpressure control device 140 is activated or energized and includes anexhaust port 140C that communicates with the outlet port 140B when theactuator pressure control device 140 is inactive or de-energized.Variable activation of the actuator pressure control device 140regulates or controls the pressure of the hydraulic fluid 102 as thehydraulic fluid 102 communicates from the inlet port 140A to the outletport 140B. The internal closed loop pressure control provides pressurefeedback within the solenoid to adjust the amount of flow to the outletport 140B based on a particular current command from the controller 32,thereby controlling pressure. The inlet port 140A is in communicationwith the main supply line 126. The outlet port 140B is in communicationwith an actuator supply line 180. The exhaust port 140C is incommunication with the sump 104 or a backfill circuit.

The actuator supply line 180 communicates pressurized hydraulic fluid102 from the actuator pressure control device 140 to a plurality of flowcontrol devices and a plurality of shift actuators. For example, theactuator supply line 180 provides a flow of pressurized hydraulic fluid102 to a first flow control device 182, a second flow control device184, a third flow control device 186, a fourth flow control device 188,as well as a first synchronizer actuator 190A, a second synchronizeractuator 190B, a third synchronizer actuator 190C, and a fourthsynchronizer actuator 190D.

The first flow control device 182 is preferably an electricallycontrolled variable force solenoid. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thefirst flow control device 182 is operable to control the flow of thehydraulic fluid 102. The first flow control device 182 includes an inletport 182A that communicates through an adjustable hydraulic orifice orrestriction with an outlet port 182B when the first flow control device182 is energized to a current greater than the null point current andincludes an exhaust port 182C that communicates with the outlet port182B when the first flow control device 182 is de-energized to a currentless than the null point current. Variable activation of the first flowcontrol device 182 regulates or controls the flow of the hydraulic fluid102 as the hydraulic fluid 102 communicates from the inlet port 182A tothe outlet port 182B or from outlet port 182B to exhaust port 182C. Theinlet port 182A is in communication with the actuator supply line 180.The outlet port 182B is in communication with a first synchronizersupply line 192. The exhaust port 182C is in communication with the sump104 or an exhaust backfill circuit.

The second flow control device 184 is preferably an electricallycontrolled variable force solenoid. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thesecond flow control device 184 is operable to control the flow of thehydraulic fluid 102. The second flow control device 184 includes aninlet port 184A that communicates through an adjustable hydraulicorifice or restriction with an outlet port 184B when the second flowcontrol device 184 is energized to a current greater than the null pointcurrent and includes an exhaust port 184C that communicates with theoutlet port 184B when the second flow control device 184 is de-energizedto a current less than the null point current. Variable activation ofthe second flow control device 184 regulates or controls the flow of thehydraulic fluid 102 as the hydraulic fluid 102 communicates from theinlet port 184A to the outlet port 184B or from outlet port 184B toexhaust port 184C. The inlet port 184A is in communication with theactuator supply line 180. The outlet port 184B is in communication witha second synchronizer supply line 194. The exhaust port 184C is incommunication with the sump 104 or an exhaust backfill circuit.

The third flow control device 186 is preferably an electricallycontrolled variable force solenoid. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thethird flow control device 186 is operable to control the flow of thehydraulic fluid 102. The third flow control device 186 includes an inletport 186A that communicates through an adjustable hydraulic orifice orrestriction with an outlet port 186B when the third flow control device186 is energized to a current greater than the null point current andincludes an exhaust port 186C that communicates with the outlet port186B when the third flow control device 186 is de-energized to a currentless than the null point current. Variable activation of the third flowcontrol device 186 regulates or controls the flow of the hydraulic fluid102 as the hydraulic fluid 102 communicates from the inlet port 186A tothe outlet port 186B or from outlet port 186B to exhaust port 186C. Theinlet port 186A is in communication with the actuator supply line 180.The outlet port 186B is in communication with a third synchronizersupply line 196. The exhaust port 186C is in communication with the sump104 or an exhaust backfill circuit.

The fourth flow control device 188 is preferably an electricallycontrolled variable force solenoid. Various makes, types, and models ofsolenoids may be employed with the present invention so long as thefourth flow control device 188 is operable to control the flow of thehydraulic fluid 102. The fourth flow control device 188 includes aninlet port 188A that communicates through an adjustable hydraulicorifice or restriction with an outlet port 188B when the fourth flowcontrol device 188 is energized to a current greater than the null pointcurrent and includes an exhaust port 188C that communicates with theoutlet port 188B when the fourth flow control device 188 is de-energizedto a current less than the null point current. Variable activation ofthe fourth flow control device 188 regulates or controls the flow of thehydraulic fluid 102 as the hydraulic fluid 102 communicates from theinlet port 188A to the outlet port 188B or from outlet port 188B toexhaust port 188C. The inlet port 188A is in communication with theactuator supply line 180. The outlet port 188B is in communication witha fourth synchronizer supply line 198. The exhaust port 188C is incommunication with the sump 104 or an exhaust backfill circuit.

The synchronizer actuators 190A-D are preferably two-area pistonassemblies operable to each engage or actuate a shift rail in asynchronizer assembly, but can be three-area piston assemblies withoutdeparting from the scope of the present invention. For example, thefirst synchronizer actuator 190A is operable to actuate the firstsynchronizer assembly 30A, the second synchronizer actuator 190B isoperable to actuate the second synchronizer assembly 30B, the thirdsynchronizer actuator 190C is operable to actuate the third synchronizerassembly 30C, and the fourth synchronizer actuator 190D is operable toactuate the fourth synchronizer assembly 30D.

The first synchronizer actuator 190A includes a piston 200A slidablydisposed within a piston housing or cylinder 202A. The piston 200Apresents two separate areas for pressurized hydraulic fluid to act upon.The piston 200A engages or contacts a finger lever, shift fork, or othershift rail component 203A of the first synchronizer assembly 30A. Thefirst synchronizer actuator 190A includes a fluid port 204A thatcommunicates with a first end 205A of the piston 200A and a fluid port206A that communicates with an opposite second end 207A of the piston200A having a smaller contact area than the first end 205A. Fluid port204A is in communication with the first synchronizer supply line 192 andfluid port 206A is in communication with the actuator supply line 180.Accordingly, the pressurized hydraulic fluid 102 communicated from theactuator pressure control device 140 enters the first synchronizeractuator 190A through the fluid port 206A and contacts the second end207A of the piston 200A and the flow of hydraulic fluid 102 from thefirst flow control device 182 enters the first synchronizer actuator190A through the fluid port 204A and contacts the first end 205A of thepiston 200A. The difference in the force generated by the pressure ofthe hydraulic fluid 102 delivered to fluid port 206A from the actuatorpressure control device 140 acting on end 207A and the force generatedby the pressure of hydraulic fluid 102 delivered to fluid port 204A fromthe first flow control device 182 acting on end 205A moves the piston200A between various positions. Each position in turn corresponds to aposition of the shift rail of the first synchronizer assembly 30A (i.e.,engaged left, engaged right, and neutral). A fork position sensor 210Amay be included to communicate to the controller 32 the position of theshift fork 203A.

The second synchronizer actuator 190B includes a piston 200B slidablydisposed within a piston housing or cylinder 202B. The piston 200Bpresents two separate areas for pressurized hydraulic fluid to act upon.The piston 200B engages or contacts a finger lever, shift fork, or othershift rail component 203B of the second synchronizer assembly 30B. Thesecond synchronizer actuator 190B includes a fluid port 204B thatcommunicates with a first end 205B of the piston 200B and a fluid port206B that communicates with an opposite second end 207B of the piston200B having a smaller contact area than the first end 205B. Fluid port204B is in communication with the second synchronizer supply line 194and fluid port 206B is in communication with the actuator supply line180. Accordingly, the pressurized hydraulic fluid 102 communicated fromthe actuator pressure control device 140 enters the second synchronizeractuator 190B through the fluid port 206B and contacts the second end207B of the piston 200B and the flow of hydraulic fluid 102 from thesecond flow control device 184 enters the second synchronizer actuator190B through the fluid port 204B and contacts the first end 205B of thepiston 200B. The difference in force generated by the pressure of thehydraulic fluid 102 delivered to fluid port 206B from the actuatorpressure control device 140 acting on end 207B and the force generatedby the pressure of the hydraulic fluid 102 delivered to fluid port 204Bfrom the second flow control device 184 acting on end 205B moves thepiston 200B between various positions. Each position in turn correspondsto a position of the shift rail of the second synchronizer assembly 30B(i.e., engaged left, engaged right, and neutral). A fork position sensor210B may be included to communicate to the controller 32 the position ofthe shift fork 203B.

The third synchronizer actuator 190C includes a piston 200C slidablydisposed within a piston housing or cylinder 202C. The piston 200Cpresents two separate areas for pressurized hydraulic fluid to act upon.The piston 200C engages or contacts a finger lever, shift fork, or othershift rail component 203C of the third synchronizer assembly 30C. Thethird synchronizer actuator 190C includes a fluid port 204C thatcommunicates with a first end 205C of the piston 200C and a fluid port206C that communicates with an opposite second end 207C of the piston200C having a smaller contact area than the first end 205C. Fluid port204C is in communication with the third synchronizer supply line 196 andfluid port 206C is in communication with the actuator supply line 180.Accordingly, the pressurized hydraulic fluid 102 communicated from theactuator pressure control device 140 enters the third synchronizeractuator 190C through the fluid port 206C and contacts the second end207C of the piston 200C and the flow of hydraulic fluid 102 from thethird flow control device 186 enters the third synchronizer actuator190C through the fluid port 204C and contacts the first end 205C of thepiston 200C. The difference in the force generated by the pressure ofthe hydraulic fluid 102 delivered to fluid port 206C from the actuatorpressure control device 140 acting on end 207C and the force generatedby the pressure of the hydraulic fluid 102 delivered to fluid port 204Cfrom the third flow control device 186 acting on end 205C moves thepiston 200C between various positions. Each position in turn correspondsto a position of the shift rail of the third synchronizer assembly 30C(i.e., engaged left, engaged right, and neutral). A fork position sensor210C may be included to communicate to the controller 32 the position ofthe shift fork 203C.

The fourth synchronizer actuator 190D includes a piston 200D slidablydisposed within a piston housing or cylinder 202D. The piston 200Dpresents two separate areas for pressurized hydraulic fluid to act upon.The piston 200D engages or contacts a finger lever, shift fork, or othershift rail component 203D of the fourth synchronizer assembly 30D. Thefourth synchronizer actuator 190D includes a fluid port 204D thatcommunicates with a first end 205D of the piston 200D and a fluid port206D that communicates with an opposite second end 207D of the piston200D having a smaller contact area than the first end 205D. Fluid port204D is in communication with the fourth synchronizer supply line 198and fluid port 206D is in communication with the actuator supply line180. Accordingly, the pressurized hydraulic fluid 102 communicated fromthe actuator pressure control device 140 enters the fourth synchronizeractuator 190D through the fluid port 206D and contacts the second end207D of the piston 200D and the flow of hydraulic fluid 102 from thefourth flow control device 188 enters the fourth synchronizer actuator190D through the fluid port 204D and contacts the first end 205D of thepiston 200D. The difference in the force generated by the pressure ofthe hydraulic fluid 102 delivered to fluid port 206D from the actuatorpressure control device 140 acting on end 207D and the force generatedby the pressure of the hydraulic fluid 102 delivered to fluid port 204Dfrom the fourth flow control device 188 acting on 205D moves the piston200D between various positions. Each position in turn corresponds to aposition of the shift rail of the fourth synchronizer assembly 30D(i.e., engaged left, engaged right, and neutral). A fork position sensor210D may be included to communicate to the controller 32 the position ofthe shift fork 203D.

During general operation of the hydraulic control system 100, theaccumulator 130 provides the pressurized hydraulic fluid 102 throughoutthe system and the pump 106 is employed to charge the accumulator 130.Selection of a particular forward or reverse gear ratio is achieved byfirst selectively actuating one of the synchronizer assemblies 30A-D andthen selectively actuating one of the torque transmitting devices 22,24. It should be appreciated that which actuator assembly 30A-D andwhich torque transmitting device 22, 24 provide which forward or reversegear ratio may vary without departing from the scope of the presentinvention.

Generally, the actuator pressure control device 140 provides pressurizedhydraulic fluid 102 to each of the synchronizer actuators 190A-D andeach of the flow control devices 182, 184, 186, and 188. Individualsynchronizer actuators 190A-D are actuated by controlling a flow fromone of the flow control devices 182, 184, 186, and 188 while maintaininga flow from the remaining flow control devices to keep the unengagedsynchronizer actuators in a neutral position.

For example, to actuate the first synchronizer assembly 30A, theactuator pressure control device 140 is energized to provide a pressureon the piston 200A and to provide a flow of hydraulic fluid 102 to thefirst flow control device 182. Bi-directional translation of the firstsynchronizer assembly 30A is then achieved by selectively energizing thefirst flow control device 182. For example, energizing the first flowcontrol device 182 to provide a flow of hydraulic fluid 102 to thesynchronizer actuator 190A which provides a pressure acting on thepiston end 205A that is sufficient to overcome the force generated bythe pressure acting on the piston end 207A from the actuator pressurecontrol device 140 moves the piston 200A to a first engaged position.After controlling the piston back to neutral typically through closedloop position control, energizing the first flow control device 182 toprovide a flow of hydraulic fluid 102 to the synchronizer actuator 190Awhich provides a pressure acting on the piston end 205A that is balancedwith the force generated by the pressure acting on the piston end 207Afrom the actuator pressure control device 140 maintains the piston 200Ain a neutral or unengaged position. Energizing or de-energizing thefirst flow control device 182 to provide a flow of hydraulic fluid 102to the synchronizer actuator 190A which provides a pressure acting onthe piston end 205A that is insufficient to overcome the force generatedby the pressure acting on the piston end 207A from the actuator pressurecontrol device 140 moves the piston 200A to a second engaged position.

To actuate the second synchronizer assembly 30B, the actuator pressurecontrol device 140 is energized to provide a pressure on the piston 200Band to provide a flow of hydraulic fluid 102 to the second flow controldevice 184. Bi-directional translation of the second synchronizerassembly 30B is then achieved by selectively energizing the second flowcontrol device 182. For example, energizing the second flow controldevice 184 to provide a flow of hydraulic fluid 102 to the synchronizeractuator 190B which provides a pressure acting on the piston end 205Bthat is sufficient to overcome the force generated by the pressureacting on the piston end 207B from the actuator pressure control device140 moves the piston 200B to a first engaged position. After controllingthe piston back to neutral typically through closed loop positioncontrol, energizing the second flow control device 184 to provide a flowof hydraulic fluid 102 to the synchronizer actuator 190B which providesa pressure acting on the piston end 205B that is balanced by the forcegenerated by the pressure acting on the piston end 207B from theactuator pressure control device 140 maintains the piston 200B in aneutral or unengaged position. Energizing or de-energizing the secondflow control device 184 to provide a flow of hydraulic fluid 102 to thesynchronizer actuator 190B which provides a pressure acting on thepiston end 205B that is insufficient to overcome the force generated bythe pressure acting on the piston end 207B from the actuator pressurecontrol device 140 moves the piston 200B to a second engaged position.

To actuate the third synchronizer assembly 30C, the actuator pressurecontrol device 140 is energized to provide a pressure on the piston 200Cand to provide a flow of hydraulic fluid 102 to the third flow controldevice 186. Bi-directional translation of the third synchronizerassembly 30C is then achieved by selectively energizing the third flowcontrol device 186. For example, energizing the third flow controldevice 186 to provide a flow of hydraulic fluid 102 to the synchronizeractuator 190C which provides a pressure acting on the piston end 205Cthat is sufficient to overcome the force generated by the pressureacting on the piston end 207C from the actuator pressure control device140 moves the piston 200C to a first engaged position. After controllingthe piston back to neutral typically through closed loop positioncontrol, energizing the third flow control device 186 to provide a flowof hydraulic fluid 102 to the synchronizer actuator 190C which providesa pressure acting on the piston end 205C that is balanced by the forcegenerated by the pressure acting on the piston end 207C from theactuator pressure control device 140 maintains the piston 200C in aneutral or unengaged position. Energizing or de-energizing the thirdflow control device 186 to provide a flow of hydraulic fluid 102 to thesynchronizer actuator 190C which provides a pressure acting on thepiston end 205C that is insufficient to overcome the force generated bythe pressure acting on the piston end 207C from the actuator pressurecontrol device 140 moves the piston 200C to a second engaged position.

To actuate the fourth synchronizer assembly 30D, the actuator pressurecontrol device 140 is energized to provide a pressure on the piston 200Dand to provide a flow of hydraulic fluid 102 to the fourth flow controldevice 188. Bi-directional translation of the fourth synchronizerassembly 30D is then achieved by selectively energizing the fourth flowcontrol device 188. For example, energizing the fourth flow controldevice 188 to provide a flow of hydraulic fluid 102 to the synchronizeractuator 190D which provides a pressure acting on the piston end 205Dthat is sufficient to overcome the force generated by the pressureacting on the piston end 207D from the actuator pressure control device140 moves the piston 200D to a fourth engaged position. Aftercontrolling the piston back to neutral typically through closed loopposition control, energizing the fourth flow control device 188 toprovide a flow of hydraulic fluid 102 to the synchronizer actuator 190Dwhich provides a pressure acting on the piston end 205D that is balancedby the force generated by the pressure acting on the piston end 207Dfrom the actuator pressure control device 140 maintains the piston 200Din a neutral or unengaged position. Energizing or de-energizing thefourth flow control device 188 to provide a flow of hydraulic fluid 102to the synchronizer actuator 190D which provides a pressure acting onthe piston end 205D that is insufficient to overcome the force generatedby the pressure acting on the piston end 207D from the actuator pressurecontrol device 140 moves the piston 200D to a second engaged position.

To engage or actuate the first torque transmitting device 22, the firstclutch pressure control device 136 and the first clutch flow controldevice 144 are energized. To engage or actuate the second torquetransmitting device 24, the first clutch pressure control device 136 andthe second clutch flow control device 160 are energized. Typically theengagement is monitored and controlled with position sensors (notshown).

In an alternate embodiment of the present invention, the first andsecond flow control devices 144 and 160 are replaced with first andsecond pressure control devices (or a combination of flow and pressurecontrol devices). The first and second pressure control devices arepreferably electrically controlled variable force solenoids havinginternal closed loop pressure control. The pressure control solenoidsare operable to vary the pressure acting on the clutch actuators 156 and168 to engage and disengage the clutches 22 and 24.

In yet another alternate embodiment of the present invention, the first,second, third, and fourth flow control devices 182, 184, 186, and 188are replaced with first, second, third, and fourth pressure controldevices (or a combination of flow and pressure control devices). Thefirst, second, third, and fourth pressure control devices are preferablyelectrically controlled variable force solenoids having internal closedloop pressure control. The pressure control solenoids are operable tovary the pressure acting on the synchronizer actuators 190A-D.

By providing flow control of the clutches 22 and 24 and/or thesynchronizer assemblies 30A-D, the hydraulic control system 100 isoperable to provide direct clutch position control, direct synchronizeractuator position control, and variable clutch and synchronizer actuatorposition control. At the same time, quick clutch response times areenabled, spin losses are reduced, and packaging space of the hydrauliccontrol system 100 is reduced, all of which contributes to improved fueleconomy and performance. The hydraulic control system 100 is alsocompatible with BAS/BAS+ hybrid systems. Finally, failure modeprotection is enabled through pre-staged position control of the controldevices 136, 140, 144, 160, 182, 184, 186, and 188.

Referring further to FIGS. 3 through 7, the operation of theelectro-hydraulic control system 100 (FIGS. 2A and 2B) for the dry dualclutch transmission 10 (FIG. 1) will be described. Recall, theelectro-hydraulic control system 100 includes three main subsystems: anoil delivery subsystem 101, a clutch control subsystem 103, and asynchronizer control subsystem 105. The main components of the oildelivery subsystem 101 are the electrically-driven, fixed-displacementpump 106, the blow-off safety valve 116, the high pressure side filter118 with a blow-off feature 120, the pump check ball arrangement 124,the pressure accumulator 130, and the pressure sensor 132.

The electrically-driven, fixed displacement pump 106 is employed toprovide pressurized hydraulic fluid 102 to actuate clutches 22, 24 andthe synchronizers 30A-D to make the transmission 10 shift. The pump 106provides pressurized fluid independent of whether the engine is running,thereby keeping the clutches 22, 24 staged for quick response duringengine start/stop maneuvers. The pump 106 is turned on when the pressuresensor 132 indicates that the accumulator 130 needs to be recharged andis turned off when full charge pressure is achieved. The pump 106 mayalso run at a fixed lower rpm to create a closed-loop pressure controlduring certain failsafe operation modes where a failed clutch solenoidcould result in over pressurization of the clutch. The pump 106 can beturned on during shifting events where relatively large amounts ofhydraulic volume are extracted from the accumulator 130. The pump 106can also be turned on prior to the driver starting the engine tohydraulically charge the system before any shifting or drive-away isrequested. This can be triggered by the opening of a door, unlocking ofthe car doors, or other means.

FIG. 3 shows a process 300 for controlling the oil delivery subsystem101. Prior to initial charging of the hydraulic control system 100, theoil side of the accumulator 130 is depressurized in an initial startstep 302. The accumulator piston is pushed by the gas charge pressure tothe bottom of its respective bore, such that no reserve oil volume isemployed by the transmission 10 for shifting. The pressure sensor 132sends a signal to the TCM 32 (FIG. 1) to start the electric motordriving the pump 106 in a step 304. In a step 306, the pump 106accelerates to a fixed rpm and begins displacing hydraulic fluid fromthe sump, out through the oil filter 118 and check ball arrangement 120,124, and into the accumulator 130. This oil builds pressure and beginsto push the accumulator piston against the gas charge. The relationshipof pressure to displaced volume is governed by law of physics for gases.The pressure sensor 132 determines the system pressure (P) in a step308.

Referring also to FIG. 4, which shows a typical charge and dischargecycle for accumulator pressure versus time, when the system pressure (P)reaches a predetermined value (P1) as reported by the pressure sensor132 to the TCM 32 (step 310), the current to the electric pump 106 isshut off causing it to stop spinning in a step 314, and if P is lessthan P1, the process 300 returns to step 308. At this point oil wants torush from the accumulator 130 back into the pump 106 but is preventedfrom doing so by the check ball arrangement 124 which seats and sealsthe pump 106 from the accumulator 130. With the check ball arrangement124 seated, the only place for the accumulator oil to flow is to therest of the subsystems 103 and 105 for clutch and synchronizer control.The leakage of these subsystems and oil volume used to stroke actuatorsmakes the pressure in the accumulator 130 decrease over time. Thepressure sensor 132 continues to monitor the system pressure (P) in astep 316, and once the pressure sensor 132 reports a pressure below apre-determined recharge pressure P2 in a step 318, the pump 106 iscommanded to turn to repeat the charge cycle (steps 320 and 306). Thepre-determined restart or recharge pressure P2 is calculated as afunction of temperature, gas charge pressure in the accumulator, pumpoutput flow capabilities, and either learned or assumed leakage andstroke volumes to engage and neutralize forks and clutches. Inparticular, the pump restart or recharge pressure is determined bycalculating the accumulator pressure level that will guaranty sufficientaccumulator volume in reserve to accomplish a number of rapid shiftingmaneuvers. The reserve volume is the volume stored in the accumulator130 between the recharge pressure P2 and a minimum pressure P3. Thereserve volume required is a function of the number of shifts, thecomponent volumes stroked, the shift times, the rate of system leakage,and the rate of pump output. Once the reserve volume is determined, thepump recharge pressure can be calculated according to the law of physicsfor gases. When the pump 106 is restarted at the recharge pressure P2,the worst case flow event (that is, supported shift) is protectedagainst by the reserved volume stored in the accumulator 130.

The blow-off safety valve 116 is designed to unseat and limit the systempressure in the event that the pump 106 does not shut off at the righttime because of a failed pump motor, a failed pressure sensor, orsluggish response. The designed blow-off pressure is slightly above themaximum expected system pressure. For example, if the maximum systempressure is 60 bar, the blow-off may be set at a nominal value of about80 bar.

The oil delivery subsystem 101 supplies pressurized hydraulic fluid tothe clutch control subsystem 103 to actuate the two clutches 22, 24. Inthis embodiment, the clutch control subsystem 103 includes a pressurecontrol solenoid (PCS) 136 fed by the oil delivery system 101. The PCS136 feeds flow control solenoids (FCS) 144, 160, which in turn feedrespective clutch piston assembly or actuators 152, 168. Each clutchactuator 152, 168 has a position sensor which relates the actuator'sposition back to the TCM 32 to be used in creating a clutch torque toposition relationship. In this way the clutch torque is controlled usingposition as the independent variable.

A process 400 for controlling the clutch control subsystem 103 is shownin FIG. 5. After starting the process 400 in a step 402, the requiredtorque capacity is determined in a step 404, and the clutch torque toposition relationship is determined in a step 406 as the transmission isoperating by relating the reported engine torque while the clutch isslipping to the position reported by the clutch position sensor. Thisrelationship, once learned, is used to provide a feed-forward controlcommand while shifting. Closed-loop control is also used to fine tunethe clutch torque shift profile.

The commanded pressure level of the PCS 136 is calculated from thehigher of two pressure requirements. The first is the pressure levelrequired to provide the requested amount of flow. The second is thepressure level required to hold the requested amount of clutch torque.As a note, in most cases the pressure level commanded is higher than thepressure required to maintain torque capacity, though it follows thetrend of required clutch torque capacity. The pressure is higher becausethe flow control solenoids 144 and 160 prefer a constant pressure dropacross the valve to obtain predictable flow rates through the valve.Once this pressure level is commanded in a step 408, it establishes oneside of the pressure potential across the flow control solenoids 144,160. The PCS 136 has a performance characteristic that relates regulatedpressure to commanded electrical current. Once the commanded pressure isdetermined, the appropriate amount of current can be commanded in a step410.

Each of the flow control solenoids 144, 160 can be thought of as avariable orifice. The solenoids 144, 160 have a relationship betweenvalve flow area and electrical current. Once a pressure potential issupplied across the solenoid, the relationship becomes flow rate versuselectrical current. These solenoids are capable of both positive (feed)flow and negative (exhaust) flow depending on the value of currentcommanded. The downstream side of the pressure potential across eachsolenoid 144, 160 is the clutch pressure. By knowing the position of theclutch 22 or 24 in a step 412, an estimate of clutch pressure can bemade in a step 414. This is subtracted from the pressure command of thePCS 136 to establish the pressure potential across the respective FCS.With the known pressure potential across the FCS, a predictable flowrate to current relationship can be used for commanding the FCSs 144,160. The proper current can then be commanded on the FCS to produce thefeed-forward component of the control flow in a step 416. Closed loopcontrol is also used based on actual and commanded piston velocity andposition to achieve the target clutch position.

If the clutch 22 or 24 is being engaged, flow is positive and largercurrents are commanded. If the clutch 22 or 24 is being disengaged, flowis negative and lower currents are commanded. There is a region ofcurrent in the middle where the flow is deadheaded, and hence the FCS isneither feeding nor exhausting.

A spring loaded check ball arrangement 146, 162 may be provided inparallel to the FCSs 144, 160, respectively, to allow quick releases ofthe clutches 22, 24 or to release the clutch 22 or 24 in the event of aparticular FCS sticking in the deadheaded region. The clutch is releasedthrough the check ball arrangement 146, 162 by reducing the PCS pressurebelow the clutch pressure level and check ball threshold.

In this particular embodiment, the even and odd clutch circuits areidentical but independent. Each circuit's pressure level and flow ratecan be independently commanded based on the specific shifting or stagingneeds of that clutch.

The synchronizer control subsystem 105 includes a single PCS 140, fourflow control solenoids (FCSs) 182, 184, 186, 188, and four dual-actingfork actuators 190A, 190B, 190C, 190D, each with its own position sensor210A, 210B, 210C, 210D, respectively. Each fork actuator is dual-acting;that is, it has a fully-engaged position to the left, a neutral positionin the middle, and a fully engaged position to the right when referringto FIGS. 2A and 2B. For example, one actuator piston could engage the3^(rd) gear synchronizer to the left and the 5^(th) gear to the rightwith a neutral position in the middle.

Synchronizer modes include two steady-state modes and at least threetransient modes. Steady-state modes include fully engaged andneutralized modes, and the transient modes include a pre-sync 450 mode,a synchronizing 460 mode, and a post-sync 470 mode, as shown in FIG. 6,with respect to the fork position command (FP), actual synchronizerposition (SP), synchronizer force (SF), and closed-loop PID control(CL).

The output of the PCS 140 splits into eight parallel channels. Four ofthese channels feed the four FCSs 182, 184, 186, 188. The remaining fourchannels are directed to the appropriate fork actuators 190A, 190B,190C, 190D. The output of each FCS 182, 184, 186, 188 is also routed tothe appropriate fork actuator 190A, 190B, 190C, 190D, respectively. Eachof the actuators 190A, 190B, 190C, 190D has an actuator piston 200A,200B, 200C, 200D, respectively, with two opposing areas of differentsize. The larger area is connected to the output from a respective FCS182, 184, 186, 188. The smaller area is connected the output from thePCS 140.

If the actuator 190A, 1908, 190C, or 190D is desired to move to theright, the PCS 140 is commanded to a pressure level and the respectiveFCS 182, 184, 186, or 188 is commanded to a position where it will feedPCS oil to the larger area of the actuator piston 200A, 200B, 200C, or200D. Pressure builds up in the larger area, and eventually anequilibrium force is reached. Beyond this equilibrium force, the piston200A, 200B, 200C, or 200D begins to move to the right against a detentspring load and PCS pressure force generated on the smaller opposingarea. If the actuator is desired to move to the left, the PCS 140 iscommanded to an appropriate pressure level and the FCS 182, 184, 186, or188 is commanded to a position where it will exhaust the oil in thelarger area of the actuator piston 200A, 200B, 200C, or 200D. Aspressure drops in the larger area, eventually an equilibrium force isreached. Beyond this equilibrium force, the piston 200A, 200B, 200C, or200D begins to move to the left because of the detent spring load andPCS pressure force generated on the smaller opposing area.

The command of the PCS pressure and FCS position is dependent on themode of operation. Referring to FIG. 7A, a process 500 for operating thesynchronizer control subsystem 105 is shown. After the process 500commands a synchronizer engagement (step 502) of one or more of thesynchronizers 30A, 30B, 30C, and 30D, the TCM 32 commands the branchcontrols to execute a pre-sync event in a step 504. This event includesmoving the actuator piston 200A, 200B, 200C, or 200D and fork 203A,203B, 203C, or 203D until the synchronizer sleeve contacts and indexesthe blocker ring. The TCM 32 controls the synchronizer movement by useof closed-loop position and velocity feedback from the position sensor210A, 210B, 210C, or 210D. In a step 506, the PCS 140 is commanded to apressure level sufficient to provide the flow rate required and overcomethe detent spring and piston drag. And also in the step 506, the FCS182, 184, 186, or 188 is commanded to open to either feed or exhaust thelarger area volume depending on the desired direction. These commandsare adjusted as dictated by the closed-loop position control.

As the actuator piston 200A, 200B, 200C, or 200D approaches the learnedposition at which synchronization begins, the velocity of the piston isslowed to avoid a bump or clunk when synchronizer contact is made.Pressure from the PCS 140 is reduced in a step 508 in preparation forthe beginning of the synchronization phase of the shift. Once thebeginning of synchronization is signaled using position sensor 210A,210B, 210C, or 210D and speed sensor feedback in a step 510, the FCS182, 184, 186, or 188 is opened further in a step 512 so it is no longerthe significant restriction in the circuit. This allows the controllingforce on the piston to be just a function of the output of the PCS 140.If the desired synchronization force is to the right, the FCS 182, 184,186, or 188 opens up to feed. This equalizes the pressure on both sidesof the piston 200A, 200B, 200C, or 200D, but since the larger areaprovides a larger force than the smaller area, there is a net force tothe right. If the desired synchronization force is to the left, the FCS182, 184, 186, or 188 opens up to exhaust. This drops the pressure onthe large side of the piston 200A, 200B, 200C, or 200D, but since thesmaller area is still pressurized, there is a net force to the left.

The actuator force through the synchronization phase is ramped toprovide a smooth speed change across the synchronizer 30A, 30B, 30C, or30D without any clunks or bumps. As the synchronization nears the end,as determined in a decision step 514, the pressure is lowered in a step516 in anticipation of the post-sync phase. In the post-sync phase, theblocker ring indexes and allow the sleeve to move through to fullengagement with the gear. This is controlled with closed-loop positionand velocity control. The velocity of the fork actuator 190A, 190B,190C, or 190D is controlled to avoid a clunk when the sleeve contactsand stops on the gear. The control of the PCS 140 and FCS 182, 184,186,188 during post-sync phase is similar to the pre-sync phase where apressure level is set with the PCS 140 and the FCS 182, 184, 186, 188 isopened to either feed or exhaust to control the velocity of the piston200A, 200B, 200C, 200D.

Once full engagement is achieved as determined in a decision step 518,the PCS pressure drops to zero pressure as active control of the FCS182, 184, 186, or 188 is maintained in a step 520. This ensures that thefork 203A, 203B, 203C, or 203D remains in full engagement. Back taper onthe synchronizer teeth and the detent spring force hold the synchronizer30A, 30B, 30C, or 30C in full engagement. Since changes in PCS pressureimpart a force change on each of the four actuators 190A, 190B, 190C,190D, the closed-loop position controls the FCSs 182, 184, 186, 188 atall times that the PCS 140 is active. This ensures that the forks 203A,203B, 203C, 203D do not move out of their intended positions when asynchronizer movement is initiated.

Referring now to FIG. 7B, a process 600 for disengaging thesynchronizers 30A, 30B, 30C, 30D is shown. After the process 600 beginsin a step 602, when disengaging the synchronizer 30A, 30B, 30C, or 30Dfrom full engagement back to neutral, there is only a position andvelocity controlled phase. The FCS 182, 184, 186, or 188 is openedeither to feed or exhaust depending on the direction of the intendedmotion in a step 604. The PCS 140 is commanded to a pressure levelrequired to generate the commanded flow across the FCS 182, 184, 186, or188 in a step 606. At this point the FCS 182, 184, 186, or 188 iscommanded to direct oil into or out of the large area chamber, forcingthe respective piston 200A, 200B, 200C, or 200D to move. The positionand velocity of the actuator piston 200A, 200B, 200C, or 200D iscontrolled via closed-loop control using the feedback of the positionsensor 210A, 210B, 210C, or 210D. As the fork 203A, 203B, 203C, or 203Dapproaches the middle neutral position, the commanded velocitydecreases. Once the position has reached a region near the learnedneutral position, the PCS 140 is profiled off in a step 608 while stillactively controlling the FCS 182, 184, 186, or 188. Once the pressure isexhausted on the actuator 190A, 190B, 190C, or 190D, the mechanicaldetent spring holds the actuator 190A, 190B, 190C, or 190D in theneutral position to disengage the respective synchronizer 30A, 30B, 30C,or 30D in a step 610. Again, since changes in PCS pressure impart aforce change on each of the four actuators 190A, 190B, 190C, 190D, theclosed-loop position controls the FCSs 182, 184, 186, 188 at all timesthat the PCS 140 is active. This ensures that the forks 203A, 203B,203C, 203D do not move out of their intended positions when asynchronizer movement is initiated.

The description of the invention is merely exemplary in nature andvariations that do not depart from the general essence of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

1. A method of controlling a dual clutch and a plurality ofsynchronizers in a transmission, the method comprising: selectivelyactuating the dual clutch with a first clutch actuator subsystem that isin downstream fluid communication with a clutch pressure controlsolenoid, the clutch pressure control solenoid being in downstream fluidcommunication with a source of pressurized hydraulic fluid; selectivelyactuating the dual clutch with a second clutch actuator subsystem thatis in downstream fluid communication with the clutch pressure controlsolenoid; controlling the pressure of the hydraulic fluid to the firstand the second clutch actuator subsystems so that each clutch of thedual clutch engages with a desired torque; and actuating the pluralityof synchronizers with a plurality of actuators, wherein each of theplurality of actuators is in downstream communication with asynchronizer pressure control solenoid and each of the plurality ofactuators is in downstream communication with a respective one of first,second, third, and fourth synchronizer control solenoids, each of thefirst, second, third, and fourth synchronizer control solenoids being indownstream fluid communication with the synchronizer pressure controlsolenoid, and wherein each of the plurality of synchronizers is engagedby controlling the flow of hydraulic fluid from the first, second,third, and fourth synchronizer control solenoids to the plurality ofactuators.
 2. The method of claim 1 further comprising controlling thepressure of hydraulic fluid that is communicated to the first and thesecond clutch actuator subsystems with the clutch pressure controlsolenoid, and further comprising controlling the pressure of hydraulicfluid that is communicated to each of the first, second, third, andfourth control synchronizer solenoids and to each of the plurality ofactuators with the synchronizer pressure control solenoid.
 3. The methodof claim 1 further comprising controlling the first, second, third, andfourth synchronizer control solenoids to control a flow of hydraulicfluid that is communicated from the synchronizer pressure controlsolenoid to the plurality of actuators.
 4. The method of claim 1 whereinthe synchronizer pressure control solenoid communicates with a firstplurality of chambers in each of the plurality of actuators and each ofthe first, second, third, and fourth synchronizer control solenoidscommunicate with one of a second plurality of chambers in each of theplurality of actuators, wherein each of the first plurality of chambersis disposed on a side of a moveable member opposite the second pluralityof chambers, and wherein the moveable members are interconnected to thesynchronizers.
 5. The method of claim 1 wherein the synchronizerpressure control solenoid includes an input in downstream fluidcommunication with the source of pressurized hydraulic fluid and anoutput, and wherein each of the first, second, third, and fourthsynchronizer control solenoids include an input in downstream fluidcommunication with the output of the synchronizer pressure controlsolenoid and an output.
 6. The method of claim 5 wherein the pluralityof actuators includes a first, a second, a third, and a fourth actuatoreach having a first input and a second input, wherein the first inputsof the first, second, third, and fourth actuators are in downstreamfluid communication with the output of the synchronizer pressure controlsolenoid, and wherein the second inputs of the first, second, third, andfourth actuators are each in downstream fluid communication with one ofthe outputs of the first, second, third, and fourth synchronizer controlsolenoids.
 7. The method of claim 1 wherein actuating the first clutchactuator subsystem includes actuating a first clutch actuator indownstream fluid communication with a first clutch flow controlsolenoid, the first clutch flow control solenoid being in downstreamfluid communication with the clutch pressure control solenoid, andwherein actuating the second clutch actuator subsystem includesactuating a second clutch actuator in downstream fluid communicationwith a second clutch flow control solenoid, the second clutch flowcontrol solenoid being in downstream fluid communication with the clutchpressure control solenoid.
 8. The method of claim 7 wherein controllingthe pressure of the hydraulic fluid to the first and the second clutchactuator subsystems includes calculating a command pressure level forthe clutch pressure control solenoid based on a clutch torque toactuator position relationship, estimating the clutch pressure of eachclutch from the position of each clutch to establish a desired pressurepotential across respective clutch flow control solenoids, and applyinga command current to each clutch flow control solenoid such that eachclutch of the dual clutch engages with the desired torque.
 9. A methodof controlling a dual clutch and a plurality of synchronizers in atransmission, the hydraulic control system comprising: selectivelyactuating the dual clutch with a first clutch actuator subsystem that isin downstream fluid communication with a clutch pressure controlsolenoid, the clutch pressure control solenoid being in downstream fluidcommunication with a source of pressurized hydraulic fluid; selectivelyactuating the dual clutch with a second clutch actuator subsystem thatis in downstream fluid communication with the clutch pressure controlsolenoid; controlling the pressure of the hydraulic fluid to the firstand the second clutch actuator subsystems so that each clutch of thedual clutch engages with a desired torque; actuating one of theplurality of synchronizers with a first actuator that is in downstreamfluid communication with a synchronizer pressure control solenoid and afirst synchronizer control solenoid, the first actuator being engaged byselectively controlling a flow of hydraulic fluid from the firstsynchronizer control solenoid; actuating one of the plurality ofsynchronizers with a second actuator that is in downstream fluidcommunication with the synchronizer pressure control solenoid and asecond synchronizer control solenoid, the second actuator being engagedby selectively controlling a flow of hydraulic fluid from the secondsynchronizer control solenoid; actuating one of the plurality ofsynchronizers with a third actuator that is in downstream fluidcommunication with the synchronizer pressure control solenoid and athird synchronizer control solenoid, the third actuator being engaged byselectively controlling a flow of hydraulic fluid from the thirdsynchronizer control solenoid; and actuating one of the plurality ofsynchronizers with a fourth actuator that is in downstream fluidcommunication with the synchronizer pressure control solenoid and afourth synchronizer control solenoid, the fourth actuator being engagedby selectively controlling a flow of hydraulic fluid from the fourthsynchronizer control solenoid
 10. The method claim 9 further comprisingcontrolling the pressure of hydraulic fluid that is communicated to thefirst and the second clutch actuator subsystems with the clutch pressurecontrol solenoid and controlling the pressure of hydraulic fluid that iscommunicated to each of the first, second, third, and fourth actuatorsand each of the first, second, third, and fourth synchronizer controlsolenoids with the synchronizer pressure control solenoid.
 11. Themethod of claim 9 further comprising controlling the first, second,third, and fourth synchronizer control solenoids to control a flow ofhydraulic fluid that is communicated from the synchronizer pressurecontrol solenoid to the first, second, third, and fourth actuators,respectively.
 12. The method of claim 9 wherein the synchronizerpressure control solenoid includes an input in downstream fluidcommunication with the source of pressurized hydraulic fluid and anoutput, and wherein each of the first, second, third, and fourthsynchronizer control solenoids include an input in downstream fluidcommunication with the output of the synchronizer pressure controlsolenoid and an output.
 13. The method of claim 12 wherein the first,second, third, and fourth actuators each include a first input and asecond input, wherein the first inputs of the first, second, third, andfourth actuators are in downstream fluid communication with the outputof the synchronizer pressure control solenoid, and wherein the secondinputs of the first, second, third, and fourth actuators are each indownstream fluid communication with one of the outputs of the first,second, third, and fourth synchronizer control solenoids, respectively.14. The method of claim 9 wherein actuating the first clutch actuatorsubsystem includes actuating a first clutch actuator in downstream fluidcommunication with a first clutch flow control solenoid, the firstclutch flow control solenoid being in downstream fluid communicationwith the clutch pressure control solenoid, and wherein actuating thesecond clutch actuator subsystem includes actuating a second clutchactuator in downstream fluid communication with a second clutch flowcontrol solenoid, the second clutch flow control solenoid being indownstream fluid communication with the clutch pressure controlsolenoid.
 15. The method of claim 14 wherein controlling the pressure ofthe hydraulic fluid to the first and the second clutch actuatorsubsystems includes calculating a command pressure level for the clutchpressure control solenoid based on a clutch torque to actuator positionrelationship, estimating the clutch pressure of each clutch from theposition of each clutch to establish a desired pressure potential acrossrespective clutch flow control solenoids, and applying a command currentto each clutch flow control solenoid such that each clutch of the dualclutch engages with the desired torque
 16. A method of controlling adual clutch and a plurality of synchronizers in a transmission, themethod comprising: actuating the dual clutch with a first clutchactuator subsystem that is in downstream fluid communication with asource of pressurized hydraulic fluid; actuating the dual clutch with asecond clutch actuator subsystem that is in downstream fluidcommunication with the source of pressurized hydraulic fluid; commandinga synchronizer pressure control solenoid to a pressure level sufficientto provide a flow rate of a hydraulic fluid, the synchronizer pressurecontrol solenoid being in downstream fluid communication with the sourceof pressurized hydraulic fluid; commanding at least one of a first,second, third, and fourth synchronizer control solenoids to open, eachof the first, second, third, and fourth synchronizer control solenoidsbeing in downstream fluid communication with the synchronizer pressurecontrol solenoid; reducing the pressure in the hydraulic fluid at thebeginning of a synchronization phase of the plurality of synchronizers;opening further the at least one of the first, second, third, and fourthsynchronizer control solenoids to selectively control the flow ofhydraulic fluid to a respective actuator of a plurality actuators, eachactuator being in downstream fluid communication with respectivesynchronizer control solenoids and the synchronizer pressure controlsolenoid; controlling the movement of respective pistons for each of theplurality of actuators to a desired position with closed-loop positioncontrol so that a desired actuator force is achieved; and actuating theplurality of synchronizers with the plurality of actuators.
 17. Themethod of claim 16 further comprising reducing the pressure of thehydraulic fluid in the plurality of synchronizer control solenoids toabout zero when a desired gear of the transmission is engaged.
 18. Themethod of claim 16 wherein actuating the first clutch actuator subsystemincludes actuating a first clutch actuator in downstream fluidcommunication with a first clutch flow control solenoid, the firstclutch flow control solenoid being in downstream fluid communicationwith a clutch pressure control solenoid, and wherein actuating thesecond clutch actuator subsystem includes actuating a second clutchactuator in downstream fluid communication with a second clutch flowcontrol solenoid, the second clutch flow control solenoid being indownstream fluid communication with the clutch pressure controlsolenoid.
 19. The method of claim 18 wherein controlling the pressure ofthe hydraulic fluid to the first and the second clutch actuatorsubsystems includes calculating a command pressure level for the clutchpressure control solenoid based on a clutch torque to actuator positionrelationship, estimating the clutch pressure of each clutch from theposition of each clutch to establish a desired pressure potential acrossrespective clutch flow control solenoids, and applying a command currentto each clutch flow control solenoid such that each clutch of the dualclutch engages with the desired torque.